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how to upload separately selected files in form POST request? [duplicate]

This question already has answers here:
Uploading multiple files using formData()
(18 answers)
Closed 5 years ago.
What I want
People click add image button, they select an image, image is added to gallery.
They can delete images by clicking cross sign and re click add image button to add more images.
This all works, I've a reference to all File elements.
However, I can't figure out how to send the files in post request of form.
Problem the problem is that You can't create FileList out array of file, or set array of files as input.files = arrOfFiles.
Input element itself doesn't let you add more files, or remove files... it simply replaces old file with new file(s).
which is not what i want therefore i'm keep reference to file objects in js, and letting user remove images or add more.
I know i can send individual file as XHR, but I want to send them through form that already exists.
I wanted to know a way to send files through form not js, but apparently that's not possible

That's exactly what the FormData API is for: create from scratch a form's data that you will be able to upload to your server as if it were created from a <form> object, except that you can control what goes there or not.
So to append a File or a Blob in a FormData, the code is
var fd = new FormData();
fd.append(field_name, blob, file_name);
To append multiple files, you can call again fd.append, but note that backend often need to have the field_name formatted in such a way they can know multiple values are expected here.
Usually this is done by adding [] after your fieldname.
var fd = new FormData();
fd.append('files[]', blob_1, file_name_1);
fd.append('files[]', blob_2, file_name_2);
And then you can send it through an AJAX request to your server, which won't make the difference between this request and a real one made froma single <input multiple name="files[]">.
Note that in case of File, file_name is optional and will default to the File's name if not set. However, it is needed for Blobs if you don't want a random name to be set.
var file_1 = new File(['foo'], 'file1.txt',{type:'text/plain'});
var file_2 = new File(['bar'], 'file2.txt', {type:'text/plain'});
var fd = new FormData();
fd.append('files[]', file_1);
fd.append('files[]', file_2);
console.log(...fd.entries());
// and to send it to your server
var xhr = new XMLHttpRequest();
xhr.open('POST', 'your_server_url');
xhr.send(fd);

If you are just going to upload images. Consider using base64 encoding. That is what I did. Assign base64 encoded URL to stringify JSON, or whatever you wish that is easier for you.
When the data is POST-ed, do the conversion there, to get back your files for saving them. Decoding base64 will be dependent on your backend language though of which you did not mention in your question.
In JavaScript, you can use this function to load up the image in preview state like you mentioned.
function previewImage (inputId, eleId) {
if (window.FileReader) {
var oPreviewImg = null, oFReader = new window.FileReader(),
rFilter = /^(?:image\/bmp|image\/cis\-cod|image\/gif|image\/ief|image\/jpeg|image\/jpeg|image\/jpeg|image\/pipeg|image\/png|image\/svg\+xml|image\/tiff|image\/x\-cmu\-raster|image\/x\-cmx|image\/x\-icon|image\/x\-portable\-anymap|image\/x\-portable\-bitmap|image\/x\-portable\-graymap|image\/x\-portable\-pixmap|image\/x\-rgb|image\/x\-xbitmap|image\/x\-xpixmap|image\/x\-xwindowdump)$/i;
oFReader.onload = function (oFREvent) {
if (!oPreviewImg) {
var newPreview = document.getElementById(eleId);
oPreviewImg = new Image();
oPreviewImg.style.width = (newPreview.offsetWidth).toString() + "px";
oPreviewImg.style.height = (newPreview.offsetHeight).toString() + "px";
if(newPreview.children.length > 0)
newPreview.replaceChild(oPreviewImg, newPreview.children[0]);
else
newPreview.appendChild(oPreviewImg);
}
oPreviewImg.src = oFREvent.target.result;
// Add Bootstrap's img-thumbnail class to the image frame
oPreviewImg.classList.add("img-thumbnail");
};
return function () {
var aFiles = document.getElementById(inputId).files;
if (aFiles.length === 0) { return; }
if (!rFilter.test(aFiles[0].type)) { alert("You must select a valid image file!"); return; }
oFReader.readAsDataURL(aFiles[0]);
}
}
if (navigator.appName === "Microsoft Internet Explorer") {
return function () {
document.getElementById(eleId).filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = document.getElementById(inputId).value;
}
}
};
Then you can extract the base64 URL from the src attribute of the img element.
You may come out with your own preferred method of "cancelling" your upload by maybe destroying the img element.

Reading image into JS to subsequently compress it

I'm a server-side dev who's new to front-end development. I've been tinkering around with vanilla Javascript and need to clarify some concepts.
The usecase I'm experimenting with is handling image upload (and mid-air JS-facilitated compression before said upload to server) via JS.
Currently I'm stuck on step one. Imagine the following simple set up:
<form method="POST" action="some_url">
<input type="file" id="browse_image" onchange="compressImage(event)">
<input type="submit" value="Submit">
</form>
My question is:
At what step do I try to pass the image to a JS function (given my goal is to compress it and send it to the server)? Would this happen at the time of image selection (i.e. pressing the browse button), or at the point of pressing Submit? Where do I put the event and how do I proceed from there? A quick illustrative answer with a an example would be great!
I've been trying to do it at the point of image selection (to no avail):
function compressImage(e){
var reader = new FileReader();
reader.readAsDataURL(e.target.files[0]);
console.log(reader);
}
Would be great to get a conceptual walkthrough, alongwith a quick illustrative example. Vanilla JS only, I'm not going to touch JQuery before I get the hang of JS.

In my mind (but it's a bit subjective), you would do it in both places.
User selects a File from your input
You process the file through js
If your processing failed (e.g the file was not an image / corrupted / who knows) you can let the user know directly.
If the processing succeeded, when user clicks submit, you overwrite the default behavior of your form, and send a FormData containing your new File/Blob instead of the original one.
var toSend = null, // here we will store our processed File/Blob (the one to send)
browse_image = document.getElementById('browse_image');
// when user selects a new File
browse_image.onchange = process_user_file;
// when user decides to send it to server
document.querySelector('form').onsubmit = overwrite_default_submit;
// grab the file from the input and process it
function process_user_file(evt) {
// since we attached the event listener through elem.onevent,
// 'this' refers to the input
var file = this.files[0];
// here do your compression, for demo, we'll just check it's a png file
var reader = new FileReader();
// a FileReader is async, so we pass the actual checking script as the onload handler
reader.onload = checkMagicNumber;
reader.readAsArrayBuffer(file.slice(0,4));
}
// we don't want the real form to be submitted, but our processed File/Blob
function overwrite_default_submit(evt) {
// block the form's submit default behavior
evt.preventDefault();
// create a new form result from scratch
var form = new FormData();
// add our File/Blob
form.append("myfile", toSend, browse_image.files[0].name);
// create a new AJAX request that will do the same as original form's behavior
var xhr = new XMLHttpRequest();
xhr.open('POST', evt.target.action);
// xhr.send(form); // uncomment to really send the request
console.log('sent', toSend);
}
// simply checks if it's really a png file
// for you, it will be your own compression code,
// which implementation can not be discussed in this answer
function checkMagicNumber(evt) {
var PNG = '89504e47';
var arr = new Uint8Array(evt.target.result);
var header = "";
for(var i = 0; i < arr.length; i++) {
header += arr[i].toString(16);
}
// some user friendly actions
if(header !== PNG) {
alert('not a png file'); // let the user know it didn't work
browse_image.value = ""; // remove invalid File
sub.disabled = true; // avoid the form's submission
toSend = null; // nothing to send
}
else {
toSend = browse_image.files[0]; // for demo we don't actually modify it...
sub.disabled = false; // allow form's submission
}
}
<form method="POST" action="some_url">
<label>Please select a .png file</label>
<input type="file" id="browse_image" name="myfile">
<input type="submit" value="Submit" disabled id="sub">
</form>
Ps: note that even your original code wouldn't have sent anything, since no input in your form had a name attribute.

How do I upload images to Craigslist with Javascript + Chrome console? [duplicate]

How can I set the value of this?
<input type="file" />

You cannot set it to a client side disk file system path, due to security reasons.
Imagine:
<form name="foo" method="post" enctype="multipart/form-data">
<input type="file" value="c:/passwords.txt">
</form>
<script>document.foo.submit();</script>
You don't want the websites you visit to be able to do this, do you? =)
You can only set it to a publicly accessible web resource as seen in this answer, but this is clearly not the same as a client side disk file system path and it's therefore useless in that context.

You can't.
The only way to set the value of a file input is by the user to select a file.
This is done for security reasons. Otherwise you would be able to create a JavaScript that automatically uploads a specific file from the client's computer.

Not an answer to your question (which others have answered), but if you want to have some edit functionality of an uploaded file field, what you probably want to do is:
show the current value of this field by just printing the filename or URL, a clickable link to download it, or if it's an image: just show it, possibly as thumbnail
the <input> tag to upload a new file
a checkbox that, when checked, deletes the currently uploaded file. note that there's no way to upload an 'empty' file, so you need something like this to clear out the field's value

You can't. And it's a security measure. Imagine if someone writes JS that sets file input value to some sensitive data file?

I have write full example for load URL to input file, and preview
you can check here
1
https://vulieumang.github.io/vuhocjs/file2input-input2file/
in short you can use this function
function loadURLToInputFiled(url){
getImgURL(url, (imgBlob)=>{
// Load img blob to input
// WIP: UTF8 character error
let fileName = 'hasFilename.jpg'
let file = new File([imgBlob], fileName,{type:"image/jpeg", lastModified:new Date().getTime()}, 'utf-8');
let container = new DataTransfer();
container.items.add(file);
document.querySelector('#file_input').files = container.files;
})
}
// xmlHTTP return blob respond
function getImgURL(url, callback){
var xhr = new XMLHttpRequest();
xhr.onload = function() {
callback(xhr.response);
};
xhr.open('GET', url);
xhr.responseType = 'blob';
xhr.send();
}

As everyone else here has stated: You cannot upload just any file automatically with JavaScript.
HOWEVER! If you have access to the information you want to send in your code (i.e., not C:\passwords.txt), then you can upload it as a blob-type, and then treat it as a file.
What the server will end up seeing will be indistinguishable from someone actually setting the value of <input type="file" />. The trick, ultimately, is to begin a new XMLHttpRequest() with the server...
function uploadFile (data) {
// define data and connections
var blob = new Blob([JSON.stringify(data)]);
var url = URL.createObjectURL(blob);
var xhr = new XMLHttpRequest();
xhr.open('POST', 'myForm.php', true);
// define new form
var formData = new FormData();
formData.append('someUploadIdentifier', blob, 'someFileName.json');
// action after uploading happens
xhr.onload = function(e) {
console.log("File uploading completed!");
};
// do the uploading
console.log("File uploading started!");
xhr.send(formData);
}
// This data/text below is local to the JS script, so we are allowed to send it!
uploadFile({'hello!':'how are you?'});
So, what could you possibly use this for? I use it for uploading HTML5 canvas elements as jpg's. This saves the user the trouble of having to open a file input element, only to select the local, cached image that they just resized, modified, etc.. But it should work for any file type.

the subject is very old but I think someone can need this answer!
<input type="file" />
<script>
// Get a reference to our file input
const fileInput = document.querySelector('input[type="file"]');
// Create a new File object
const myFile = new File(['Hello World!'], 'myFile.txt', {
type: 'text/plain',
lastModified: new Date(),
});
// Now let's create a DataTransfer to get a FileList
const dataTransfer = new DataTransfer();
dataTransfer.items.add(myFile);
fileInput.files = dataTransfer.files;
</script>

You need to create a DataTransfer and set the .files property of the input.
const dataTransfer = new DataTransfer();
dataTransfer.items.add(myFile);//your file(s) reference(s)
document.getElementById('input_field').files = dataTransfer.files;

Define in html:
<input type="hidden" name="image" id="image"/>
In JS:
ajax.jsonRpc("/consulta/dni", 'call', {'document_number': document_number})
.then(function (data) {
if (data.error){
...;
}
else {
$('#image').val(data.image);
}
})
After:
<input type="hidden" name="image" id="image" value="/9j/4AAQSkZJRgABAgAAAQABAAD/2wBDAAgGBgcGBQgHBwcJCQgKDBQNDAsLDBkSEw8U..."/>
<button type="submit">Submit</button>

Actually we can do it.
we can set the file value default by using webbrowser control in c# using FormToMultipartPostData Library.We have to download and include this Library in our project. Webbrowser enables the user to navigate Web pages inside form.
Once the web page loaded , the script inside the webBrowser1_DocumentCompleted will be executed.
So,
private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
FormToMultipartPostData postData =
new FormToMultipartPostData(webBrowser1, form);
postData.SetFile("fileField", #"C:\windows\win.ini");
postData.Submit();
}
Refer the below link for downloading and complete reference.
https://www.codeproject.com/Articles/28917/Setting-a-file-to-upload-inside-the-WebBrowser-com

How to detect source filetype in JavaScript

Quite simply, is there anyway to detect what file type a source file is?
Context:I have an HTML5 audio element and depending on what button someone clicks I want to randomly change the source of that audio element using JavaScript (please, no jQuery solutions) so that different songs will play. I have several hundred sound files, so I really don't want to have to convert them all to one file type.
I currently have a method that gets a random but always correct file name via a RNG but no way of knowing the file extension this file is (it could be .ogg, .wav, .m4a or .mp3). It just tries every possible extension until one works but am having a bit of trouble with the error handling which is causing other issues to occur so it would be really great if you could help me out here with a better solution. Thanks!

// fileInput is an HTML input element: <input type="file" id="myfileinput" multiple>
var fileInput = document.getElementById("myfileinput");
// files is a FileList object (similar to NodeList)
var files = fileInput.files;
var file;
// loop trough files
for (var i = 0; i < files.length; i++) {
// get item
file = files.item(i);
//or
file = files[i];
alert(file.type);
}
developer.mozilla link

You can use a mixture of the new XMLHttpRequest Level 2 API and File API to check the file type of a server resource.
For example, to get the type of an image:
url = '/favicon.ico';
xhr = new XMLHttpRequest();
xhr.open('GET', url, true);
xhr.responseType = 'blob';
xhr.onreadystatechange = function () {
if (xhr.readyState == 4) {
var file = this.response;
alert(file.type);
}
};
xhr.send();
JSFIDDLE demo

javascript read from a txt file and inject text into form

I apologize in the advance as I am a total beginner.
I have a pre-existing html form with text fields. I need to have a button that will allow me to upload a txt file (since when trying to look for answer about this, I learned javascript can't just access a file from my PC without me actively uploading it). Then I need the values from this txt file inserted into the text fields (for example, the form has: name, last name, phone etc - and the file will fill out this info).
I am going crazy trying to collect bits and pieces from other people's questions. any help would be greatly appreciated!

it depends on how you would like to have this handled, there are basically two options:
File Upload and page redirect
you could provide a file upload form to upload your textfile, redirect to the same page via form submission, handle the data on serverside (e.g. parse the file and get the values out of it) and let the server inject the values as default properties for the form file which is returned to the browser
XMLHttpRequest File Upload
in modern browsers, the native xhr object supports an upload property, so you could send the file via that upload property. it has to be sent to a serverside script that parses the file and returns the values in a fitting format, e.g. json (which would look like this: {'name':'somename', 'lastName':'someothername'}). then you have to register an eventlistener on completion of this upload (e.g. onload) and set these values on javascript side.
check this out for XMLHttpRequest upload (better solution in my opinion): https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Using_XMLHttpRequest#Submitting_forms_and_uploading_files
edit:
well, the easiest solution would be just to provide a textfield and paste the content of the file into this field, hit a button and the content is parsed. then you wouldn't rely on network traffic or even a serverside handling, but could do everything with javascript, e.g. like this:
dom:
<textarea id="tf"></textarea>
<button id="parse">fill form!</button>
js:
var tf = document.getElementById("tf");
document.getElementById("parse").addEventListener("click", function(){
var formData = JSON.parse(tf.value);
//if your textfile is in json format, the formData object now has all values
});
edit: from the link i posted in the comments:
<!-- The HTML -->
<input id="the-file" name="file" type="file">
<button id="sendfile">send</button>
and
document.getElementById('sendfile').addEventListener("click", function(){
var fileInput = document.getElementById('the-file');
var file = fileInput.files[0];
var formData = new FormData();
formData.append('file', file);
var xhr = new XMLHttpRequest();
// Add any event handlers here...
xhr.open('POST', '/upload/path', true);
xhr.onreadystatechange = function(){
if(xhr.readyState == 4 && xhr.status == 200){
var values = JSON.parse(xhr.responseText);
//these are your input elements you want to fill!
formNameInput.setAttribute('value', values.name);
formFirstNameInput.setAttribute('value', values.firstName);
}
}
xhr.send(formData);
});
as already said, your serverside has to parse the file and respond with json